Not applicable.
Not applicable.
The invention relates to an exhaust muffler for a fuel-operated heating device, of half-shell construction with upper and lower housing half shells and also with an exhaust gas through-duct and absorption and reflection chambers, particularly for stationary heating devices or booster heaters for motor vehicles, in which the exhaust muffler can be connected to an exhaust pipe of the heating device.
According to the state of the art, exhaust mufflers for motor vehicles are known in two different application variants.
In one application variant, the exhaust muffler serves to reduce the combustion noise of a motor vehicle internal combustion engine. The exhaust muffler, e.g. an after-muffler, is situated in the exhaust gas line of the internal combustion engine.
In the other application variant of an exhaust muffler of the kind considered here, the exhaust muffler serves to reduce the combustion noise of fuel-operated vehicle supplementary heating devices in the form of booster heaters and standstill heaters. The exhaust muffler is then usually a separate component, i.e., separated from the heating device proper, and is situated in the exhaust pipe of the heating device. Booster heaters and standstill heaters are operated with liquid fuel (diesel or gasoline) and are water heating devices or air heating devices. Booster heaters are heating devices, which contribute, when the motor vehicle engine is operating, to improving the heat output to the vehicle interior and to the engine. Standstill heating devices are heating devices which also make heat output available to the vehicle independently of the engine, particularly when the vehicle is stationary, even when the vehicle engine is not running.
The invention has as its object to provide an exhaust muffler of the kind mentioned at the beginning, which enriches the state of the art of the said second application variant, particularly by the provision of an exhaust muffler which is of very simple and compact construction and nevertheless effects optimum damping, even in the low frequency region.
This object is attained by an exhaust muffler for a fuel-operated heating device of half-shell construction, comprising upper and lower housing half shells, an exhaust gas through-duct, and absorption and reflection chambers, in which the exhaust muffler is connectable to an exhaust pipe of the heating device, wherein the exhaust gas through-duct comprises an inlet pipe of an absorption chamber, a reflection chamber following the absorption chamber, and an outlet pipe, the inlet pipe comprises a perforated outer surface, an S-shaped curved section and a straight end section, the outlet pipe comprises a straight pipe having an outer surface and an inlet section and is closed on its outer surface, and the straight end section of the inlet pipe runs parallel to, and is spaced from, the inlet section of the outlet pipe.
A development of the invention is a particular construction of an exhaust muffler of the second application variant. The exhaust muffler is characterized by an exhaust gas through-duct, which is constituted by an inlet pipe of a single absorption chamber, a following single reflection chamber, and an outlet pipe. The inlet pipe is perforated on the outer surface side and has a S-shaped curvature section and a straight end section, while the output pipe is straight and is closed, i.e. unperforated, on the outer surface side. The straight end section of the inlet pipe runs parallel to, and at a spacing from, an inlet section of the output pipe. The absorption chamber and the reflection chamber are separated from one another by a vertical partition.
The inlet pipe preferably has an inlet opening, which is situated in coaxial extension of the outlet pipe and is aligned with an outlet opening of the outlet pipe.
The S-shaped curved section of the inlet pipe can be connected directly to the inlet opening of the inlet pipe.
The S-shaped curved section has in particular a straight intermediate section, the longitudinal axis of which forms an angle of preferably 45xc2x0 to the longitudinal axis of the outlet pipe.
In a particular variant, the outlet pipe is about twice as long as the straight end section of the inlet pipe.
Between the inlet pipe and the outlet pipe there is formed an angled partition which is vertical with respect to the separating plane of the housing half shells of the exhaust muffler, and which extends predominantly transversely through the whole internal space of the exhaust muffler and separates the absorption chamber from the reflection chamber.
The angled partition also extends partially about centrally between the inlet pipe and outlet pipe in the longitudinal direction of the exhaust muffler, i.e., in the direction of the longitudinal axis of the outlet pipe.
In particular, the angled partition bordering on the housing half shells has, in the region of the S-shaped curved section, a first angled end section which extends about parallel to the axis of the curved section, preferably straight and at an angle of 45xc2x0 to the axis of the outlet pipe; a planar middle section, which extends parallel to the axis of the outlet pipe; and also, in the region of an outlet opening of the inlet pipe, a second angled end section which runs at right angles to the middle section and is drawn over an outer edge of an outlet opening of the inlet pipe.
The middle section and the second angled end section of the partition have perforations, while the first angled end section of the partition forms a closed surface.
At least the inlet pipe can be constructed from two half shells which are connected together in their parting plane by a shell fold.
The housing half shells of the exhaust muffler have preferably stamped shaped creases.
In particular, each housing half shell can have a central shaped crease, which positively supports the outlet pipe on the lower or upper side in the region of its inlet opening.
Shaped creases of the housing half shells can also support the inlet pipe at the end(s), preferably with the interposition of sound-damping material which is arranged in the absorption chamber.
Shaped creases which do not contact the inlet pipe and the outlet pipe can be constituted in the housing half shells.
In a particular form of the invention, the absorption chamber can have at least two compression molded parts of sound damping material, particularly of glass fiber material; the one compression molded part fills a space of the lower housing half shell and, after insertion of the inlet pipe, the other compression molded part fills an upper space of the upper housing half shell.
The inlet opening of the inlet pipe can have an unperforated peripheral edge into which an exhaust pipe of the heating device can be positively inserted positively and sealingly connected.
The outlet opening of the outlet pipe, positively supported and sealed on the peripheral edge of the housing half shells, can be arranged set back within the interior of the exhaust muffler, and the peripheral edge of the housing half shells can be provided with an outer support surface on which an outer end pipe of the exhaust muffler is positively set and which can be connected to the outlet pipe.
Special production advantages result when the upper and lower housing half shells are of like construction.
Like or symmetrically constructed housing half shells and aligned arrangement of the inlet opening of the inlet pipe with respect to the outlet opening of the outlet pipe make possible in particular a simple laterally inverted mounting of the exhaust muffler in an exhaust pipe of the heating device. In this case, the exhaust gas throughflow runs through the exhaust muffler in the reversed direction.
The invention provides an effective construction of an exhaust muffler for a heating device, the known sound damping and silencing and sound insulation mechanisms of absorption, reflection, and interference being advantageously used while maintaining the counter-pressure which is critical for the heating device. This relates in particular to the internal structure of the exhaust muffler. However, the outer surface shells are also shaped favorably from the standpoint of acoustic technology, the formation of resonant members being prevented. The constructional shape of the exhaust muffler is chosen, and preferably ascertained by research, so that operating noises are effectively reduced, and in fact at all the power levels of a heating device which can be operated at several power levels.
Admittedly, there are possibly individual features of the invention which are known in vehicle mufflers of the first application variant mentioned at the beginning, i.e., in exhaust mufflers connected to internal combustion engines. However, the characteristics of the exhaust noise of heating devices differs substantially in its characteristics from the exhaust noise of vehicles. The exhaust noise of heating devices is a wide-band, uniform noise which results from the burning of a flame and the operation of a fan. The exhaust noise of vehicles, on the contrary, is a strongly pulsating noise, which results from the four-stroke operating mode of an internal combustion engine. For this reason, vehicle mufflers and heating device mufflers cannot be compared with each other. Seemingly similar constructional modes of vehicle mufflers thus cannot be consulted for comparison.
The manner of operation of the heating device exhaust muffler is as follows.
The heating device in its operating state develops a noise, which is brought about by the combustion of an air-fuel mixture. The exhaust gas stream is conducted through the exhaust muffler interpolated in the exhaust gas line of the heating device. The acoustic energy is hereby partially eliminated. The exhaust gas enters the exhaust muffler and is conducted in a perforated pipe, namely the inlet pipe. The perforated pipe is situated in an absorption chamber, i.e., it is surrounded on all sides with a sound-absorbing material. At the outlet of the perforated pipe, the gas enters a reflection chamber. An abrupt change in cross section occurs here. In the reflection chamber, the exhaust gas is deflected oppositely to its original flow direction and reaches the inlet of a closed pipe, namely the outlet pipe, which has a minimum excess length, i.e., at least one pipe section, parallel at the same axial height of the perforated pipe. The exhaust gas stream thus comes out of the reflection chamber into the closed pipe, and is finally conducted out of the exhaust muffler. The absorption and reflection chambers are separated from each other by a partition. The outer surface shells are embodied with a convex curvature. They include shaped creases, among other things. The throughflow direction of the exhaust muffler can also be reversed.